1. Field of the Invention
The present invention relates to a vibration driven motor and, more particularly, to a linear shaped vibration wave driven motor for urging an elastic member in which a travelling wave is formed against a rail shaped stator, and moving the elastic member along the rail shaped stator.
2. Related Background Art
As a conventional linear shaped vibration driven motor of this type, a motor shown in FIGS. 6 and 7 is known.
An elliptic metal elastic member 1 has a projection la formed on the sliding surface side, and a piezo-electric element 2 is bonded on the upper surface of the elastic member, thus forming a vibrator. When an AC voltage is applied to the piezo-electric element 2, a travelling vibration wave is formed. The generation principle of the travelling vibration wave and the structure of the piezo-electric element 2 are known to those who are skilled in the art, and a detailed description thereof will be omitted. Briefly speaking, when AC voltages having 90.degree. time phases are applied to two groups of driving piezo-electric elements, which are positionally shifted by 90.degree., of the piezo-electric element, a travelling vibration wave is formed. A rail shaped stator 8 is in frictional contact with the elastic member 1. The stator 8 is fixed to a bottom plate 10 of a motor case, and is in contact with the elastic member 1 by a compression spring 3 through a vibration insulating member (e.g., felt) 5. A planar supporting plate 6 is fixed to the elastic member 1. The central portion of the supporting plate 6 is fixed by a block shaped 10 supporting member 7, and the supporting plate 6 supports the elastic member 1.
The elastic member 1 is supported on a base 4 through the supporting plate 6 and the supporting member 7, and the base 4 is supported by restriction members 9 for restricting displacements other than that in a prospective moving direction B.sub.Y.
When a travelling vibration wave is formed in the elastic member 1, the elastic member 1 is moved along the rail shaped stator 8 by the frictional force between the rail shaped stator 8 and the elastic member 1, and the base 4, and other members 3, 5, 6, and 7 are moved in the direction By along the restriction members 9 accordingly. The frictional driving force generated in this case is applied on a portion of the elastic member 1, and is shifted from the supporting portion. For this reason, a moment acts on the elastic member 1, and the elastic member 1 is forced to shift in the directions B.sub.X and B.sub.Y.
The supporting plate 6 has an X shape, as shown in FIG. 8, and its four distal ends are joined to the inner side surfaces of the elastic member 1 by, e.g., spot welding. The central portion of the supporting plate 6 is rigidly clamped by the supporting member 7, and the supporting member 7 is fixed to the base 4. For this reason, even when the moment acts on the elastic member 1, the elastic member 1 can be smoothly linearly moved together with the base 4 without being rotated or cluttering.
Since this motor can perform position control of an intermittent driving operation with high precision, it is proposed to use the motor as a print head driving source in, e.g., a thermal jet printer. The print head is mounted on a carriage (not shown) attached to the base 4, and is linearly and reciprocally moved.
However, in the above-mentioned prior art, since the rail shaped stator 8 and the restriction members 9 are separately formed, and are elongated in the direction B.sub.y, the rail shaped stator and the restriction members can deform considerably. For this reason, it is difficult to form the rail sliding surface and the carriage guide portion of the restriction members with a high degree of precision and flatness.
Furthermore, since the bottom plate 10 attached with these rail shaped stator and restriction members is a thin plate, it can deform considerably (e.g., warps). When the restriction members 9 and the rail shaped stator 8 are attached to this bottom plate, deformation of these members is worse.
For this reason, the parallelness of the carriage guide surfaces of the two restriction members 9 is impaired, and the inclination of the carriage locally changes upon movement of the carriage in the direction B.sub.Y. As a result, the gap between the rail sliding surface and the carriage also changes.
As described above, since the elastic member 1 is attached to the carriage through the supporting member, and the compression spring 3 is also attached to the carriage, when the gap between the rail sliding surface and the carriage locally changes in the direction B.sub.y, the compression force to be applied to the elastic member 1 varies. Thus, a stable driving force for the motor cannot be obtained. When the inclination of the carriage locally changes, since the vibrator is inclined accordingly, a contact state between the rail sliding surface and the vibrator deteriorates, thus reducing motor performance.